In printers--such as dot-matrix printers--of the type including a movable printer-head carriage, it is necessary to provide a driving arrangement for selectively moving the print-head carriage in the forward and reverse directions along and relative to a printable substrate-supporting roller or other base. For this purpose, arrangements incorporating a drive motor, opposed driving and reversal pulleys, and a belt or rope or other pulling means trained about the opposed rollers and connected to the print-head carriage are well known. Bidirectional operation of the drive motor rotates the pulleys in the forward and reverse directions whereby the encircling belt is longitudinally displaced and carries the carriage to selected positions along the printable-substrate support. It is also known in such arrangements to mount the reversal pulley to a carrier housing which rests against a spring-loaded tensioning wedge for suitably stretching or otherwise tensioning the belt.
Also common in such arrangements is the provision of a slit disc which rotates in synchronism with the bidirectional rotation of the shaft of the drive motor or with one of the drive and reversal pulleys. The slit disc is scanned by a beam of light so as to generate print-head carriage path-dependent pulses which are utilized for dynamically sensing or computing the then-current position of the carriage. Other, alternative arrangements for continuously determining the present position of the moving print-head carriage are also known such, for example, as the use of a stepping-motor drive for the belt-encircling pulleys.
Such tensioning arrangements for a belt-like pulling means or displacement transmission member of a print-head carriage drive device in typewriters or similar office machines are disclosed, by way of example, in Federal Republic of Germany Laid Open Patent Application No. OS 33 19 671. For purposes of this description it is assumed that a substantially precise adjustment of the position of the print-head carriage is rendered possible by such arrangements upon both forward and reverse travel or displacement of the print-head carriage.
It is also common in printers of this type to provide or include additional elements that also require driven movement or displacement in the operation of the printer or typewriter or other office machine. Thus, for example, such apparatus typically include an inked ribbon in conjunction with which printed characters or symbols are generated and transferred to the printable substrate by the print-head. Apparatus heretofore known in the art carries out the movement or displacement of such additional parts or elements through the provision of separate drive motors and pulling means and the like. This results in substantial duplications of components in the printing apparatus, increasing manufacturing costs and decreasing the operational efficiency and, in some cases, the reliability of the apparatus.